1. Field of the Invention
The present invention relates to a bubbling system to be used as either a cleaning system for cleaning water of rivers or lakes or an oil-water separating system for separating oil in water. More particularly, the present invention relates to a bubbling system for use in either a cleaning system using the floating separation method or an oil-water separating system.
2. Description of the Prior Art
According to the cleaning method resorting to the existing floating separation, a flocculating agent is poured into stock water to be cleaned and is stirred in a flocculating bath. After this, a portion of the flocculated and stirred liquid is extracted and has air dissolved therein to prepare pressure water. This pressure water is mixed again with the remaining flocculated and stirred liquid to stick the air bubbles to the floc in the liquid so that the floc is lifted together with the air bubbles to flow into a separating bath. Moreover, an oil-water separation is also carried out by a similar method, in which air bubbles are stuck to the oil mixed in the water.
The cleaning or the oil-water separation using the floating separation makes use of the sticking action of the air bubbles which are produced from the pressure water containing the dissolved air, as described above. This bubble sticking action higher as the pressure changes more extensively when the bubbles expand and break in the water. This pressure change is the wider for smaller bubbles, as the pressure of the water is higher. On the other hand, the sticking action of the bubbles higher for a larger the more content of the air dissolved in the water, as the pressure of the water becomes higher. It is therefore concluded that the floating effect by the sticking of the bubbles is higher for the higher pressure of the water.
In the existing floating separation described above, however, the pressure water having the air dissolved therein has already released its pressure at the instant when it is mixed with the flocculated and stirred liquid, so that the air dissolved in the water changes into the air bubbles and its air content drops. At the same time, as a result of the pressure drop, moreover, the bubbles have expanded to reduce the pressure change at the time of expansion and breakage of the bubbles in the flocculating/stirring bath. Thus, a sufficient floating action cannot be attained by the sticking of the bubbles. Still the worse, the system used in the existing floating separation has to be a closed one which requires: the flocculating/stirring bath for injecting and stirring the flocculating agent into the stock water to be cleaned; and the floating separation bath for floating and separating the bubbles of the air dissolved in the pressure water by sticking them to the flock. As a result, the system has its size enlarged and is limited in its place and movement. Thus, the system is difficult to use in positions other than the specified place so that it can hardly cope with the cases in which rivers or lakes are to be cleaned.